1. Field of the Invention
The present invention relates to a digital signal encoding apparatus, a digital signal decoding apparatus, a digital signal transmitting apparatus and its method, and more specifically, is applicable to a digital satellite broadcasting.
2. Description of the Related Art
A digital satellite broadcasting system using stationary satellite has been started to be used. In FIG. 1, numeral 600 denotes a digital satellite broadcasting system as a whole. A transmission signal S200 transmitted from a transmission antenna 200 is received and amplified by a satellite 300 to be output as a transmission signal S300. The transmission signal S300 is received by a reception antennas 400. Thereby, a broadcasting system having a wide service area which has little reception interference due to obstacles on the ground can be realized. The digital satellite broadcasting system uses an image compressive encoding method called moving picture experts groups (MPEG2) to multiplex a plurality of channels on one transport stream and transmit it.
In the digital satellite broadcasting system 600 shown in FIG. 2, video signals S201A to S201D and audio signals S202A to S202D are supplied from the exterior to an encoding transmitting apparatus 210. In the encoding transmitting apparatus 210, four encoding parts 220A to 220D which have the same construction are connected to a multiplexing part 250, and the video signals S201A to S201D and the audio signals S202A to S202D are input to corresponding encoding parts 220A to 220D.
A video encoding part 221 and an audio encoding part 222 included in the encoding part 220A respectively encode the video signal S201A and the audio signal S202A by using the MPEG2 method, and they are output to a transmission buffer 230 as video encoded data S221 and audio encoded data S222 respectively. The transmission buffer 230 temporarily stores the video encoded data S221 and the audio encoded data S222, and then reads out them at a predetermined timing to output them to a multiplexing part 240. The video encoding part 221 constantly checks the content by the amount of the video encoded data S221 in the transmission buffer 230 as content information S230, and controls the amount of codes to be generated of the video encoded data S221 based on the content information S230.
The multiplexing part 240 multiplexes the video encoded data S221 and the audio encoded data S222 and outputs the resultant to a multiplexing part 250 as multiplexed data S220A. The multiplexing part 250 multiplexes the multiplexed data S220A and the multiplexed data S220B to S220D respectively output from the encoding parts 220B to 220D, and outputs the resultant to a modulating part 260 as a transport stream S250. The modulating part 260 performs a predetermined modulation on the transport stream S250 and transmits the resultant via the transmission antenna 200 as a transmission signal S200.
The satellite 300 receives and amplifies the transmission signal S200, and transmits the resultant as a transmission signal S300. In a decoding receiving apparatus 410, the transmission signal S300 is received by the reception antenna 400 to be demodulated at a demodulating part 420, and is output to a separating part 430 as a transport stream S240. The separating part 430 selects one of the video encoded data and one of the audio encoded data among from the encoded data multiplexed on the transport stream S420 in accordance with selection signal S460 output from a remote controller 460, and outputs these data to a reception buffer 440 as video encoded data S431 and audio encoded data S432.
The video encoded data S431 and the audio encoded data S432 are temporarily stored in the reception buffer 440 and then they are read out at a predetermined timing to be decoded by a video decoding part 451 and an audio decoding part 452. Thereafter, they are output to a television receiver (not shown) as a video signal S451 and an audio signal S452.
Here, in the MPEG2 method, the amount of codes to be generated by an encoding processing changes depending on the pattern of each picture of image to be encoded. In short, when the pattern is complicated, the amount of codes to be generated increases, and when the pattern in simple, the amount of codes to be generated decreases. However, the transmission signals S200 and S300 are transmitted at a fixed rate, so that the transmission buffer 230 and the reception buffer 440 are provided to absorb the fluctuation of the rate.
In the digital satellite broadcasting system, so-called speckled broadcasting for broadcasting alternately a plurality of standard definition television (SDTV) channels and one high definition television (HDTV) channel in one transponder has been studied. FIG. 3 shows an example of the speckled broadcasting. In one transponder, one channel of HDTV is broadcasted in one time slot, and four channels of SDTV are broadcasted in another time slot. In this way, the SDTV and the HDTV are broadcasted changeably, so that a broadcasting using the definition depending on the program contents can be performed.
The video encoding and video decoding of the HDTV are performed by a plurality of processors for SDTV which are combined. FIG. 4 shows the decoding processing of HDTV image in a video decoding part 225 for HDTV. The HDTV screen area is divided into four areas to be parallel-processed by four decoding processors 225A to 225D so as to perform the decoding processing of HDTV which has larger data size than that of SDTV.
The video decoding part 225 consists of four decoding processors 225A to 225D for SDTV, so that it has an ability to decode four channels of SDTV at the same time. Thereby, as shown in FIG. 4, a parallel multichannel reception for decoding a plurality of SDTV at the same time by using the video decoding part 225 can be considered.
However, to perform the parallel multichannel reception in a receiving apparatus, the number of buffers equal to the number of channels of SDTV to be displayed is required. More specifically, as shown in FIG. 5, four reception buffers are required to perform the parallel multichannel reception for decoding four channels of SDTV at the same time. Thus, this case has a problem that the construction becomes complicated and the price raises.
In view of the foregoing, and object of this invention is to provide a digital signal encoding apparatus, digital signal decoding apparatus, digital signal transmitting apparatus and its method which can perform the parallel multichannel reception of SDTV with a simple construction.
The foregoing object and other objects of the invention have been achieved by the provision of a digital signal encoding apparatus, digital signal decoding apparatus, digital signal transmitting apparatus and its method, in which a transmission buffer and a reception buffer are each used as a single buffer when the first video signal is encoded and decoded. When the number N of second video signals which have the picture elements less than that of the first video signal are encoded and decoded, the transmission buffer and the reception buffer are divided into the number of the second video signals to use them as a plurality of divided transmission buffers and a plurality of divided reception buffers.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.